The present invention relates generally to air conditioning systems for multiple room structures having independently actuable heating and cooling units in each room and, more particularly, to such systems including central desk remote control capability.
In installations including a plurality of air conditioning units such as at motels, apartments, and office buildings where individual units are used for the various zones requiring cooling or heating, remote controls have been provided wherein any one or a plurality of the individual room units may be selectively rendered inoperative from a central desk control station. This ability to render zone units inoperative from a remote point is a desirable feature which permits overall economy of operation where not all rooms are occupied or in use at the same time. Unneeded units may simply be turned off. Moreover, such systems facilitate zoned temperature control. That is, the temperature of each room may individually be adjusted as desired by means of a local thermostatic control. There may further be provided user selection between heating operation, cooling operation, or fan-only operation. Examples of such central desk control systems permitting remote on and off control are disclosed in commonly-assigned Jones U.S. Pat. No. 3,871,443 and in Bryans U.S. Pat. No. 4,143,813.
Although the present invention is concerned primarily with central desk control systems providing simple on or off control of the individual room units, it may be noted that in more elaborate central desk systems remote control over heating and cooling mode operation, temperature setting, or various combinations may be provided. For example, central desk systems providing remote control of both mode and temperature are disclosed in Pratt, Jr. U.S. Pat. No. 4,174,064 and in Dawson U.S. Pat. No. 4,284,126. Central systems for remotely controlling temperature are disclosed in Bradford U.S. Pat. No. 4,077,566 and in Cleary et al. U.S. Pat. No. 4,132,355. A central system for remotely controlling mode is disclosed in commonly-assigned Pohl et al. U.S. Pat. No. 4,287,939.
While not a central desk control system, the system of Hoffman et al. U.S. Pat. No. 4,060,123 is somewhat related in that power to a room air conditioning unit may be interrupted by means of a relay in a separate energy-saving module which is controlled by a person entering or leaving the room.
A wide variety of specific types of air conditioning units have been employed in multiple room structures, and there is accordingly no intention to limit the present invention for use in combination with any particular such unit other than as set forth in the appended claims. Similarly, the term "air conditioning" is employed herein in a broad sense to mean any form of unit which alters the characteristics of room air, for example by either heating, cooling, or both, or even through humidity modification. As one example, a typical such room sized unit includes an air cooling subsystem comprising a closed circuit refrigeration system having a refrigerant evaporator in heat exchange relationship with recirculating indoor air flow, and a separate heating subsystem comprising electrical resistance heaters. As another example, the closed circuit refrigeration system may be reversible and comprise what is conventionally termed a "heat pump" to provide heating, as well as cooling, with the electrical resistance heaters being required only for supplemental purposes. Also, a reversible air valve heat pump may be employed, where the evaporator and condenser retain their usual functions relative to the closed circuit refrigeration system, but indoor and outdoor airflows are selectively directed over the evaporator and condenser.
Another feature which may be included in a room-sized air conditioning unit is a "Freeze Sentinel" circuit. A Freeze Sentinel circuit functions to energize a heating load whenever required to ensure that room temperature does not fall below a predetermined temperature, for example 40.degree. F., regardless of user control settings.
In each of the specific types of air conditioning units summarized above, it will be appreciated that there is at least one major energy-consuming load such as a refrigerant compressor motor or an electrical resistance heater. Refrigerant compressor motors are included in closed circuit refrigeration systems which provide room air cooling, and are also included in reversible cycle heat pump systems wherein a closed circuit refrigeration system selectively provides both room cooling and heating. Electrical resistance heaters are typically included as supplemental units and reversible cycle heat pump units for use when the heat pump itself is unable to satisfy the heating load, and are included as the primary heat source in non-reversible systems which selectively provide either cooling by refrigeration or heating by electrical resistance heat.
Individual room air conditioning units also typically include one or more relatively lower-power electrical load devices which do not directly provide heating or cooling energy. A typical example of such a relatively lower-power load is an electric motor driven fan used for air circulation, the term "air circulation" including ventilation through the forced introduction of outdoor ambient air. Another example of a relatively lower-power electrical load is electronic control circuitry for establishing user temperature selection and user control over heating, cooling, and fan-only operation. Especially in the context of electronic control circuitry which typically includes volatile memories for user mode selections and temperature selections, it is desirable to continuously maintain supply voltage.
In the design of such central desk control systems, easy installation and reliability of operation are important considerations. There are a number of aspects to the general problem of providing a system which is easy to install and reliable.
For example, it is increasingly common for solid state electronic controls to be employed in the individual room units, either microprocessor-based controls or controls employing discrete logic devices. It will be appreciated that such control circuitry operates normally with relatively low voltages, and is susceptible to nearly instantaneous damage in the event of any overvoltage, however momentary, or application of voltage or incorrect polarity. Moreover, in the case of control circuits having relatively high impedance levels such as may be associated with operational amplifier circuits or MOS digital logic devices, the circuits are relatively susceptible to extraneous voltage pick-up from either capacitive or inductive coupling. This is particularly so where there are extended conductor runs external to the control circuitry. Even though such induced voltages may not cause actual damage to the control circuitry, the induced voltages may be erroneously interpreted as valid control signals, resulting in faulty operation.
In a typical central desk system installation, a set of control conductors is run from each individual room unit to the central desk location. It is desirable to minimize the amount of specialized circuitry and equipment required at the central desk end of the control conductors.
Moreover, either during initial system installation or during subsequent modifications, incorrect voltages or polarities may be applied to the control conductors extending from individual room units. This is particularly likely to occur at the central desk end of the control conductors. Accordingly, it is also desirable to minimize the possibility of damage to the control circuitry in the individual room unit caused by the application of such incorrect voltage or polarities.